The present invention relates to an open-end spinning device with a spinning rotor rotating in a rotor housing.
German Patent Publication DE-OS 25 52 955 teaches rotatably supporting a spinning insert inside the spinning rotor of an open-end spinning device. The rotor shaft of the spinning rotor is designed as a hollow shaft and rotates on a support disk mounting. The drive and bearing shaft of the spinning insert, also referred to as a rotor insert, is supported in the hollow shaft by roller bearings. The spinning rotor and the spinning insert are driven by a common tangential belt and rotate in the same direction. In order to achieve a necessary speed difference between the spinning rotor and the spinning insert in such rotor spinning devices, the drive whorls of the two shafts have different dimensions. The open-end spinning device of German Patent Publication DE-OS 25 52 955 is intended to be able to eliminate disadvantages in the nature of the rotor-spun yarn such as, e.g., reduced yarn strength, that are inherent in a yarn produced with the rotor spinning method in contrast to the ring spinning method. However, open-end rotor spinning devices of this type have not proven themselves in practice.
German Patent Publication DE 44 11 342 A1 also describes an open-end spinning device with a spinning insert rotatably supported in the spinning rotor. The spinning insert can be intermittently fixed on the spinning rotor via a coupling device. In normal spinning operation the spinning insert is entrained exclusively by the yarn. This is possible because the yarn can pull the spinning insert along with itself in the direction of rotation by leading of the so-called tie-up zone at which fibers collected within the rotor groove become twisted with a trailing shank of previously formed yarn and are withdrawn therewith from the rotor through a yarn withdrawal nozzle. It is possible by means of the coupling device to accelerate the spinning insert to the rotor speed in the acceleration phase of the spinning device, i.e., during start up of the spinning device such as following a batch change or a yarn break, by entraining the spinning insert via the coupling device with the spinning rotor. This can avoid an overloading of the yarn during a piecing or start up operation that could result in a yarn break or in failure of the piecing operation. German Patent Publication DE 44 11 342 A1 states that so-called belly bands are produced by yarns that are constantly being newly fed in. These belly bands should be able to be reliably avoided if the yarn is protected relatively well from fibers exiting from the fiber guide conduit by a guide conduit in the spinning insert. However, German Patent Publication DE 44 11 342 A1 was based on insufficient data. It was not recognized that the production of belly bands does not take place in the area between the rotor groove and the withdrawal nozzle but rather during the tie-up process of the yarn in the tie-up zone, as is explained in detail, e.g., in German Patent Publication DE 199 63 087 A1. Therefore, the undesired production of belly bands with the device of German Patent Publication DE 44 11 342 A1 is not prevented or is prevented only insufficiently.
German Patent Publication DE 195 28 727 A1 shows an open-end rotor spinning machine with an external rotor in which a rotor insert, designated as an internal rotor, is arranged that is driven independently of the external rotor. The external rotor as well as the internal rotor are each caused to rotate by separate tangential belts. The rotational speed of the internal rotor is always somewhat greater than the circumferential speed of the external rotor during the operation of spinning and during yarn piecing. The fibers are drawn from the rotor groove, designated as a collector groove, via a withdrawal conduit and formed thereby into a yarn. The internal rotor is also called a stretch rotor in German Patent Publication DE 195 28 727 A1 since a certain stretching of the yarn should be able to be achieved. Between the rotor groove and the withdrawal conduit, the yarn runs through a yarn guide conduit, designated here as a yarn conduit, in the internal rotor and is guided during this time by surfaces in the yarn conduit that are curved in the direction of rotation of the rotors. The yarn conduit is designed in such a manner as to prevent fibers from the rear side (as viewed in the direction of rotation) from entering from the rotor groove. The yarn formation should take place in such a manner with the yarn conduit curved in the direction of rotation of the internal rotor and of the external rotor that no undesired belly bands, designated as cover fibers, or alternatively called string winding fibers in German Patent Publication DE 195 28 727 A1, occur. In particular, the fact that no yarns from the rear side of the yarn conduit (as viewed in the direction of rotation) can pass into the fiber bundle drawn off from the rotor groove is supposed to contribute to this effect.
However, the occurrence of cover fibers cannot be prevented with the device according to German Patent Publication DE 195 28 727 A1 for the same reasons as in the case of German Patent Publication DE 44 11 342 A1. The open-end rotor spinning machine described in German Patent Publication DE 195 28 727 A1 operates with a curvature of the yarn end in the tie-up zone oriented to extend in the same direction of rotation as the spinning rotor, referred to as a so-called leading tie-up zone. In this case, fibers coming from the fiber slide surface of the rotor that directly reach the tie-up zone of the yarn end are first joined to the rotating yarn in a direction opposite the normal direction of yarn rotation, after which the direction of rotation of these fibers changes into the main direction of rotation of the yarn during the further withdrawal of the yarn with the simultaneous rotation of the same about its own axis. In particular, when the fiber first reaches the tie-up zone with its end located in front in the direction of rotor rotation, several locally concentrated loops, i.e., the so-called belly bands, can be produced during the change of direction of rotation that results as the tie-up zone progresses. A shrinkage of the yarn occurs at this point with the consequence of non-uniformity of the yarn and of a braked propagation of rotation, which for its part results in a loss of strength in the yarn.
On the other hand, German Patent Publication DE 199 63 087 A1 describes a method of open-end rotor spinning in which of the yarn end is oriented to assume a curvature at the tie-up zone counter to the rotational direction of the spinning rotor, referred to as a so-called lagging tie-up zone. This has the consequence that individual fibers reaching the yarn end in the tie-up zone are immediately tied on or up in the normal direction of rotation of the yarn and thus do not cause any disturbance in the production of yarn with resulting quality defects. The tie-up zone consequently lags behind with a speed of rotation lessened by the speed of yarn withdrawal. As a result of this lagging of the tie-up zone the fibers are withdrawn from the rotor groove under a greater tractive stress. This creates an additional stretching that results in an improved orientation of the fibers and makes possible a greater utilization of the fiber substance strength. The yarn produced in this manner has, in contrast to a yarn produced with a leading tie-up zone, a pronounced yarn core of stretched fibers.
German Patent Publication DE 199 63 087 A1 further states that the processes could be distinctly improved in the framework of the further development of the open-end spinning methods so that normally rather large accumulations of fibers, contaminations or even a vacuum loss are avoided. It is thus the case today, it is stated, that in principle modern open-end rotor spinning machines operate without additional auxiliary aids for maintaining the curvature of the yarn end in the direction of rotor rotation.
The fact that the fibers are tied up into the yarn end with the same orientation with which they were transported through the fiber guide conduit into the spinning rotor also has an advantageous effect on the yarn structure in the case of a lagging tie-up zone. The tangential alignment of the fiber current in the direction of rotor rotation also assures a stretching of the fibers. In contrast to the known state of the art, the infeed of fibers in the direction of rotor rotation itself results in a fair stability of the yarn manufacturing process. There is also no suggestion in the method according to German Patent Publication DE 199 63 087 A1 to strive for a further stretching by the use of an internal rotor and therewith an only marginal improvement of the yarn. This marginal improvement is not worth the expense for an internal rotor.
A fairly good stability of the yarn production process results from the fiber infeed in the direction of spinning of the rotor. Since an improved stretching is achieved in the method according to German Patent Publication DE 199 63 087 A1, the need of using an inner rotor with the goal of increasing the stretching also does not result in this device. The method of German Patent Publication DE 199 63 087 can not always satisfy the current high demands as regards the stability of the spinning process.
However, it cannot be completely excluded as regards the stability of the spinning process that a spinning process with a lagging tie-up zone could change into a spinning process with a leading tie-up zone. Therefore, the method according to German Patent Publication DE 199 63 087 A1 can not always satisfy the high demands of the present time.